This invention relates to improvements in drill bits for through-the-steel drill stems.
The invention was primarily developed in connection with mine roof drilling and it is thus described herein. However, it will be readily appreciated that our improved drill bit may be used with equal facility for other drilling operations, and description of the same in relation to mine roof drilling is not to be construed as a limitation on the scope of the invention.
In mining operations, such as coal mining, it has become a widely accepted practice to support the mine roof by means of roof bolts as embedded within spaced apart holes drilled in the mine roof. Roof bolts serve to pin pieces of loose material to solid rock above, reinforce areas of the underground arch, prevent sheer movement of rock strata, and form a solid self-supporting beam of several weak strata. With each advance of the mine face additional roof bolts are required and it thus follows that there will be an extremely large number of holes drilled into the mine roof for receiving roof bolts.
It is quite naturally desirable to prevent fine respirable dust from being suspended in the air the miners must breathe. As is obvious, drilling in a mine roof is a setting conducive to dispersion of drill dust within the mine. Through-the-stem drilling is thus usually used for drilling in mines. That is, use of a hollow drill stem in which a partial vacuum is created for drawing drill cuttings thereinto and thence to a collector. Drill bits for through-the-steel drill stems are provided with drill ports through which the drill cuttings may be drawn into the through-the-steel drill stem.
Others have previously proposed various types of drill bits for use with through-the-steel drill stems. By way of examples, as shown in U.S. Pat. Nos. 3,187,825; 3,434,553; 3,434,554; 3,613,807; 4,313,506; 4,330,044; and 4,492,278.
As described in U.S. Pat. No. 4,313,506, those drill bits having ports on the sides thereof through which drill cuttings may be exhausted are necessarily elongate and also generally include work surfaces which grind the drill cuttings to a relatively fine dust-like consistency. It is apparent that the more finely divided the drill cuttings, the greater the possibility of suspension of the same in the air. Also, grinding of the drill cuttings causes the drill bit to become very hot, thus shortening its useful life.
Drill bits having side ports are also deficient in that, during the first inch or so of drilling, and until the side ports enter the drilled hole, the drill cuttings will be spewed directly into the mine.
Further, in use of drill bits having side ports, the finely divided drill dust is necessarily drawn down along the sides of the drilled holes to the side ports, with the result that at least some of such finely divided drill dust will be left clinging to the sides of the drilled hole. Drill dust as collected on the walls of the drilled hole is likely to cause slippage of a mine roof bolt of the expansion type and, where resin is used, into which the mine roof bolt is embedded, results in incomplete adherence of the resin to the side walls of the drilled holes.
We recognize that others have previously provided drill bits having drill cut receiving openings that open upwardly to the drill tip. For instance, as shown in U.S. Pat. No. 4,330,044. Such drill cut receiving openings have usually been provided either by drilling holes through the top of the bit or by use of a hollow bit having a drill tip supported thereacross. As to those having holes drilled through the top of the bit, the same do not open along a sufficient area of the cutting edges of the drill tip for efficient withdrawal of the drill cuttings directly therethrough. As to those which are hollow, the side walls thereof must necessarily be fairly thick in order to support the drill tip without fracturing, the thicker side walls reducing the area of the drill ports.
In the present invention, the body of the drill bit is unitarily formed for supporting the drill tip in a manner such that the forces of drilling torque are distributed throughout the body portion thereof instead of only at the upper extremities of the drill ports as in the drill bit of U.S. Pat. No. 4,330,044. In our drill bit a sleeve is provided about the body portion thereof to define the outer reaches of the dust collection ports.
It is thus an object of this invention to provide a drill bit having drill cut receiving ports opening directly to and along the cutting edge of the drill tip so that drill cuttings may be directly drawn thereinto without finely dividing the same and in which the size of such ports is not proscribed by side walls that are necessarily thick in order that they may support a drill tip against drilling torque.
Through-the-steel drill stems now in general use include a male keeper designed to mate with a female receptacle of the drill bit for attachment of the drill bit to the drill stem.
Such keepers are generally spring loaded toward and extend into an opening as provided through the drill bit shank. As is apparent, drill dust and other debris that is usually present in a mine may collect within the drill shank opening and become impacted thereagainst during the drilling operation in such a manner as to cause depression of the keeper, in which case the drill bit may be lost up in the drill hole.
Also, the not infrequently required removal of worn bits and connection of new ones inflicts considerable wear and tear on the keeper of the drill stem, causing it to weaken, as a result of which breaking and shearing of drill stem keepers has proven to be a constant problem.
Thus, a further object of this invention is the provision of a male keeper as mounted on the drill bit and which mates with a female receptacle of the drill stem.
Other objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, and in which drawings: